Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21832722b&link_type=abstract
American Astronomical Society, AAS Meeting #218, #327.22; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Broad iron K emission lines are not always seen in the X-ray spectra of type 1 AGN, in spite of their high accretion rates that imply an optically-thick disk extending down to at or near the innermost stable circular orbit (ISCO), and the unobscured line-of-sight to their X-ray sources. The reason for the notable lack of relativistic disk signatures in many type-1 AGN is unknown. We have made high S/N ( 600,000 counts) Suzaku observations of NGC 5548 to set tight limits on any broad Fe K line at EW<40 eV in the summed spectrum,or eV in most of the individual spectra. We compare the properties of NGC 5548 with the famously strong broad Fe K emitter MCG--6-30-15. The two AGNs are similar in several parameters (X-ray luminosity, optical-to-X-ray slope, host type), but differ strongly in black hole mass (a factor 15), radio-loudness (a factor 10, though both are formally radio-quiet) and Eddington ratio (a factor 50). The low Eddington ratio ( 2%) of NGC 5548 is close to the transition value to a jet-dominated low/hard state in X-ray binaries, where the inner accretion disk has withdrawn, which would narrow any relfected line emission. The higher radio-loudness of NGC 5548 may then be related to a nascent jet. However, this scenario is complicated by the presence of strong optical and UV emission lines indicating the presence of an optically-thick disk at small radii. We also examine where the X-ray continuum in NGC 5548 could originate in light-bending models in order to explain the lack of a broad Fe K line.
Brenneman Laura
Elvis Martin
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